<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
    xmlns="http://java.sun.com/xml/ns/javaee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>FileUploadServlet</servlet-name>
    <servlet-class>FileUploadServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>FileUploadServlet</servlet-name>
    <url-pattern>/servlet/FileUploadServlet</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>upload.html</welcome-file>
  </welcome-file-list>
</web-app

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.FileUploadBase.SizeLimitExceededException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
public class FileUploadServlet extends HttpServlet {

public FileUploadServlet() {
  super();
}
public void destroy() {
  super.destroy(); // Just puts "destroy" string in log
  // Put your code here
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  final long MAX_SIZE = 3 * 1024 * 1024;// 设置上传文件最大为 3M
  // 允许上传的文件格式的列表
  final String[] allowedExt = new String[] { "jpg", "jpeg", "gif", "txt",
    "doc", "docx", "mp3", "wma", "m4a" };
  response.setContentType("text/html");
  // 设置字符编码为UTF-8, 这样支持汉字显示
  response.setCharacterEncoding("UTF-8");
  // 实例化一个硬盘文件工厂,用来配置上传组件ServletFileUpload
  DiskFileItemFactory dfif = new DiskFileItemFactory();
  dfif.setSizeThreshold(4096);// 设置上传文件时用于临时存放文件的内存大小,这里是4K.多于的部分将临时存在硬盘
  dfif.setRepository(new File(request.getRealPath("/")
    + "ImagesUploadTemp"));// 设置存放临时文件的目录,web根目录下的ImagesUploadTemp目录
  // 用以上工厂实例化上传组件
  ServletFileUpload sfu = new ServletFileUpload(dfif);
  // 设置最大上传尺寸
  sfu.setSizeMax(MAX_SIZE);
  PrintWriter out = response.getWriter();
  // 从request得到 所有 上传域的列表
  List fileList = null;
  try {
   fileList = sfu.parseRequest(request);
  } catch (FileUploadException e) {// 处理文件尺寸过大异常
   if (e instanceof SizeLimitExceededException) {
    out.println("文件尺寸超过规定大小:" + MAX_SIZE + "字节<p />");
    out.println("<a href=\"upload.html\" target=\&